In the living body, glucose metabolism is effected by the glycolytic pathway in which an enzyme called phosphofructokinase (E.C. 2.7.1.11) (to be referred to as "PFK 1" hereinafter) plays an important role as a regulatory factor. FBP is a factor which directly activates PFK 1, and carbohydrate metabolism is regulated by the activation of PFK 1. Thus, it has been confirmed in recent years that FBP plays an important role in the living body as a carbohydrate metabolism-related factor.
In general, FBP is produced either by organic synthesis or enzymatic synthesis. In the organic synthesis process, FBP is produced, for example, by firstly synthesizing fructose 1,2-cyclic, 6-bisphosphate (to be referred to as "FCP" hereinafter) from a starting material, fructose 1,6-bisphosphate (to be referred to as "FDP" hereinafter), using dicyclohexyl carbodiimide as a catalyst. The thus synthesized FCP is subjected to partial alkali hydrolysis to form FBP (E. Van Schaftingen and H. G. Hers, European Journal of Biochemistry, vol.117, p.319, 1981; K. Uyeda, E. Fruya and A. D. Sherry, Journal of Biological Chemistry, vol.256, p.8679, 1981; and JP-A-60-161994). The term "JP-A" as used herein means an "unexamined published Japanese patent application". As an example of the enzymatic synthesis method, E. Fruya and K. Uyeda (Journal of Biological Chemistry, vol.256, p.7109, 1981) disclose a process in which FBP is produced from fructose 6-phosphate (to be referred to as "F6P" hereinafter) and adenosine 5'-triphosphate (to be referred to as "ATP" hereinafter) by the action of fructose 6-phosphate 2-kinase (E.C. 2.7.1.105) (to be referred to as "PFK 2" hereinafter).
With regard to a process for the isolation of FBP, the present inventors are not aware of any report concerning the isolation of FBP in a high yield in the form of high purity powder. A primary reason for this is that FBP is extremely unstable in aqueous solutions especially under acidic conditions, and decomposes completely within several minutes even in a weakly acidic aqueous solution. Because of this, steps for the purification of FBP cannot be effected easily. Also, when FBP is synthesized using the aforementioned organic synthesis process, conversion ratio of FCP into FBP by hydrolysis is low (about 15%), and the isolation of FBP is quite difficult because of the extremely similar physical properties of the by-product FDP to those of the product FBP. In addition, when FBP is synthesized using the aforementioned enzymatic synthesis process, the known process is disadvantageous from a practical point of view because of the low FBP production yield.